Demands for higher data rates for mobile services are steadily increasing. At the same time modern mobile communication systems as 3rd Generation systems (3G) and 4th Generation systems (4G) provide enhanced technologies, which enable higher spectral efficiencies and allow for higher data rates and cell capacities. As operators are seeking to extend the coverage and capacity of their networks advanced transmission concepts are one way forward.
Conventional mobile communication systems make use of circuit switched and packet switched data. While for circuit switched data transmission radio resources are permanently reserved in a connection oriented manner, packet data transmission makes use of scheduling, i.e. radio resources are assigned non-permanently in a connection less manner. The procedure of assigning radio resources to certain users for packet data transmission is also referred to as scheduling. The entity carrying out scheduling is also called a scheduler. Architectures of mobile communication systems tend to be more and more centralized. In other words, more and more intelligence of the mobile communication network is concentrated centralized entities and transmission points, where transmission and reception of wireless signals is carried out, become more and more lean. This kind of architecture is, for example, motivated by savings, which can be obtained at the transmission points. Since a large number of transmission points is used for a mobile communication system they may be kept as inexpensive as possible. Moreover, the efficiency of processing resources can be increased, when the processing resources are concentrated at central nodes in the network.
While processing resources are also needed for schedulers, there is a motivation to also move the schedulers to central points of the mobile communication systems. On the other hand, schedulers take into account radio conditions of mobile transceivers in the mobile communication system, which change rapidly. Therefore, there is another tendency to move the schedulers as close as possible to the wireless interface, in order to be able to quickly react to the rapidly changing conditions on the wireless interface. The farther the scheduler moves away from the wireless interface, the longer the delay for scheduling. Another point is the delay on feedback loops with a mobile transceiver, when automatic retransmission is used. In automatic retransmission transmissions are acknowledged or dis-acknowledged by respective acknowledgement packets and automatically retransmitted in case of dis-acknowledgements. The farther away the scheduler from the wireless interface, the longer the delay until such an acknowledgement packet can be received.
Stefan Brueck et al disclose in “Centralized Scheduling for Joint Transmission Coordinated Multi-Point in LTE-Advanced” a consideration of coordinated multi-point transmission/reception for LTE-Advanced as a tool to improve the coverage of high data rates, the cell-edge throughput and/or to increase the system throughput. Joint transmission schemes are an example of coordinated transmission between cells for the downlink. Here, data are transmitted simultaneously either coherently or non-coherently from multiple cells to a single mobile station. In this paper, a centralized MAC scheduling approach for joint transmission coordinated multi-point (JT CoMP) is proposed. Since several base stations transmit jointly to a single mobile station, the base stations are grouped together in so-called clusters. Several cluster strategies are investigated as well. The focus is on schemes that add only low complexity to the existing 3GPP LTE Release 8 system. Simulation results are provided for non-coherent transmission for full buffer and bursty traffic models with various system loads for different static cell clustering approaches.
Document EP 1 289 219 A1 discloses a method of scheduling data packets for transmission from a first terminal to a second terminal over a channel shared with other terminals comprising monitoring a time interval from accepting a packet for transmission and scheduling the packet for transmission. If the transmission is unsuccessful, the packet is scheduled for retransmission within a predetermined time. The predetermined time is selected dependent upon the time interval.
Document US 2009/279480 A1 discloses a method of scheduling transmissions for a base station in a multi-carrier wireless communication network which comprises scheduling initial transmissions of data packets for one or more users on a first carrier, without reserving scheduling capacity on the first carrier for retransmissions. Doing so increases the scheduled capacity of the first carrier for initial transmissions. The method further includes scheduling retransmissions, as needed, for given ones of the data packets on one or more second carriers. The method allows more traffic to be scheduled on the first carrier, meaning that multi-carrier transmissions are less frequently needed to convey all of the traffic targeted to one or more receivers. Those receivers therefore spend more time operating with a reduced receiver bandwidth (as compared to the bandwidth required for receiving more than one carrier), which reduces operating power.